Great progress has been made in the combination of micromachining and Integrated Circuit (IC) technology. Various of microelectromechanical system (MEMS) require microactuators for generating large driving force. Up to now, an electromagnetic actuator, base on electromagnetic principle, is attractive because it needs only simple fabrication process. A motor is a typical example for the electronmagnetic actuator. Generally speaking, it consists of a magnet and coils that can be made by IC planer process.
Planar coils are needed in many applications of microelectromechanical system. One example in the field of medicine is a microsystem for measuring the blood pressure inside the human body. Further, the planar coils can also be used in the generation of electromagnetic forces together with permanent magnets or permeable cores as an adjusting or driving force for micro pumps, micro valves, micro relays or other devices. Therefore, the formation of planar coils plays an important role in the making of microactuators.
One of the prior arts for fabricating the coils is described accompany with related drawings as follows (See "A NEW FABRICATION PROCESS OF A PLANAR COIL USING PHOTOSENSITIVE POLYIMIDE AND ELECTROPLATING", Y. Watanabe; The Bin International Conference on Solid State Sensors and Actuators and Eurosensors IX Stocknolm. Sweden, Jun. 25-29, 1995). Turning to FIG. 1, a ZnCu alloy substrate 2 is provided. Polyimide layer 4a, 4b are respectively coated on both sides of the substrate 2. Platinum particles 6 are formed on the surface of the top polyimide layer 4a to act as nuclei for the electroless plating. Turning to FIG. 2, a photosensitive polyimide layer 8 is then patterned on the platinum particles 6 using lithography technology. The polyimide layer 8 is cured after exposure and development process. The curing is accomplished by two steps at temperatures 140 and 350.degree. C., respectively.
As shown in FIG. 3, the substrate 2 is immersed in an alkaline copper solution of 40.degree. C. to obtain a 200 angstroms thick conductive layer 10. As shown in FIG. 4, a copper layer 12 is subsequently electroplated using copper borofluoride acid (CBA). Next, turning to FIG. 5, a polyimide layer 14 is coated on the polyimide layer 8 and the copper layer 12 for isolation. Then, a contact hole 16 is generated in the polyimide layer 14 using photolithography and etching processes. However, high manufacturing costs are associated with this prior art method.